The invention relates to a testing device for bank notes or similar legal tender in sheet form for automatic vending machines, the testing device being of the type which includes a transporting device and a testing channel equipped with scanning devices for recognizing and checking the authenticity of the bank note, the testing channel being preceded by an input channel having an adjustable width.
DE 2,747,795.A1 already discloses a document reader in which the positioning of the document during passage through the transporting channel relative to the transporting elements is set as a function of the width of the document. In other words, the transporting means characterized by rollers are stationary but the positioning of the document during transport is determined by adjustment means which set the position relative to the transporting means as a function of the width of the document. The transporting channel of the document reader through which the documents are guided during the scanning process is equipped with an adjustable side wall for a determination of either certain widths of the transporting channel or a width range for operation with documents of any desired width within this range. The scanning unit of the document reader may be preceded by an input unit, with adjustment elements for the channel width being provided in the input unit and in the scanning unit. The adjustment elements for the width of the transporting channel in the scanning unit here respond in their width setting as a function of the position of the width setting elements of the input unit. Thus separate width adjustment elements are required for the channel of the input unit and for the channel of the scanning unit which is extremely expensive from a manufacturing point of view. Since the width setting of the channels is effected in each case by changing the position of a movable side wall relative to a fixed side wall, the position of the longitudinal center axis of the channels changes correspondingly. Such a displacement of the longitudinal center axis of the channel of the scanning unit as a function of the width of the document to be checked is a drawback insofar as, for the checking of bank notes which generally have the same identifying marks at the same distance from their longitudinal center axis regardless of their width, a number of scanning devices corresponding to the number of different widths must be used for the same identifying feature on several bank notes of different widths.